Field of the Invention
This invention relates, in general, to sewing machines and, in particular, to a new and useful thread cutting device on sewing machines with a revolving looper, including a thread catcher which is actuated by double-action pneumatic cylinder and which executes a movement in one direction simultaneously gripping the needle thread and the looper thread and a movement in the other direction pulling both threads out and supplying them to a fixed knife.
Such thread cutting devices are better suited for the cutting of strong threads than those with mechanical drive by the main shaft of the machine. However, they have the disadvantage that disturbances in the synchronization of the movement of the thread catcher with the movement of the looper due to different influences on the movement sequence as a result of the independent drives of the sewing machine and the thread cutting device cannot be entirely avoided. The thread cutting device therefore does not always work quite satisfactorily; in particular, it has been found that after prolonged down time the cutting device may fail on first use.